A Photoelectrochemical Immunosensor Based on Au-Doped TiO2 Nanotube Arrays for the Detection of alpha-Synuclein

alpha-Synuclein (alpha-SYN) is a very important neuronal protein that is associated with Parkinson's disease. In this paper, we utilized Au-doped TiO2 nanotube arrays to design a photoelectrochemical immunosensor for the detection of alpha-SYN. The highly ordered TiO2 nanotubes were fabricated by using an electrochemical anodization technique on pure Ti foil. After that, a photoelectrochemical deposition method was exploited to modify the resulting nanotubes with Au nanoparticles, which have been demonstrated to facilitate the improvement of photocurrent responses. Moreover, the Au-doped TiO2 nanotubes formed effective antibody immobilization arrays and immobilized primary antibodies (Ab(1)) with high stability and bioactivity to bind target alpha-SYN. The enhanced sensitivity was obtained by using {Ab(2)-Au-GOx} bioconjugates, which featured secondary antibody (Ab(2)) and glucose oxidase (GOx) labels linked to Au nanoparticles for signal amplification. The GOx enzyme immobilized on the prepared immunosensor could catalyze glucose in the detection solution to produce H2O2, which acted as a sacrificial electron donor to scavenge the photogenerated holes in the valence band of TiO2 nanotubes upon irradiation of the other side of the Ti foil and led to a prompt photocurrent. The photocurrents were proportional to the alpha-SYN concentrations, and the linear range of the developed immunosensor was from 50 pgmL(-1) to 100 ngmL(-1) with a detection limit of 34 pgmL(-1). The proposed method showed high sensitivity, stability, reproducibility, and could become a promising technique for protein detection.